1. Field of the Invention
The present invention relates to an automatic transmission comprising an input member operatively connected to a drive source, such as a motor so as to be rotated thereby, an output member operatively connected to a driven member, a planetary gear mechanism disposed between the input and output members for transmitting power from the input member to the output member, and a centrifugally operated clutch for controlling the transmission of power between the planetary gear mechanism and the input and output members.
2. Description of the Prior Art p A planetary gear mechanism in general has gears rotating at varying speeds ranging from a low speed to a high speed, and requires a cooling means whereby frictional heat generated in meshing portions and bearing-contacting portions of these gears is absorbed to prevent seizure and deterioration of the gears. A planetary gear mechanism also requires a lubricating means for preventing the gears from being hurt or worn, and for promoting a smooth meshing and rotation of the gears to prevent a decrease in the power transmission efficiency.
A planetary gear mechanism further requires in many cases a means for minimizing the generation of noises. When a planetary gear mechanism provided with a cooling means, a lubricating means and an additional noise prevention means is installed, especially, in an automatic transmission, the construction of the automatic transmission necessarily becomes very complicated. This causes various kinds of inconveniences. Namely, it becomes necessary that the dimensions of the automatic transmission and the number of steps of manufacturing the same be increased.
In a dry type centrifugally operated clutch in general, the coefficient of friction of a lining material for a frictionally contacting portion thereof is higher than that in a wet type clutch. Therefore, in order to obtain the same clutch capacity when the clutch is rotated in a direction in which a leading effect is produced, a comparatively light, centrifugally operated weight may be satisfactorily used. However, in order to attain a stable clutch operation without accompanying a decrease in coefficient of friction of the frictionally contacting portion, it is necessary that the surface of the lining material be maintained in a perfectly dried state.
In a case where a planetary gear mechanism and a dry type centrifugally operated clutch in an automatic transmission are housed in the same casing, it is necessary that a partition wall be provided between the planetary gear mechanism and the centrifugally operated clutch for the purpose of preventing a liquid, such as a lubricating oil, which has been supplied to the planetary gear mechanism, from being deposited on the surface of a lining material for the frictionally contacting portion of the centrifugally operated clutch.
On a frictionally contacting portion of a centrifugally operated clutch, frictional heat is generated during an operation thereof. Consequently, when a dry type centrioperated clutch is employed, it is necessary that a device for absorbing the generated frictional heat be additionally provided.